1. Field of the Invention
The present disclosure relates to a photonic crystal waveguide inlet structure for improving coupling efficiency of a strip waveguide and a photonic crystal waveguide.
2. Description of the Related Art
Photonic crystal structures, that enormously reduce the sizes of photonic devices, are good alternative plans for photonic integration, and dispersion characteristic thereof is adjusted to manufacture photonic switches or photonic modulators. Strip waveguides, which are convenient to manufacture, are widely used to bring light into photonic crystal waveguides.
Recently, active research has been carried out on slow light. A group velocity of light is decreased to increase non-linear characteristic, thereby decreasing the lengths of interferometers. This allows various applications. For example, the sizes of photonic modulators can be reduced, and photonic buffers can be realized.
FIG. 1 is a schematic view illustrating structure of a photonic crystal waveguide and a strip waveguide in the related art. FIG. 2 is a view illustrating a simulation result with regard to the structure of FIG. 2. FIG. 3 is a view illustrating a case in which transmission efficiency is changed even when a little modification is made on air hole arrangement in crystal structure of a photonic crystal waveguide in the related art.
Referring to FIG. 1, in the structure of the photonic crystal waveguide and the strip waveguide, phase interference of a surface mode component generated at a junction by junction phase adjustment of a photonic crystal region improves the transmission efficiency. That is, a position where the photonic crystal waveguide contacts the strip waveguide, is adjusted to generate the surface mode in a perpendicular direction to an incident direction of light to photonic crystals, thereby improving coupling efficiency.
Referring to FIG. 2, the simulation result with regard to the structure of the photonic crystal waveguide and the strip waveguide is illustrated with an incident wave and an output wave thereof.
Referring to FIG. 3, a photonic crystal waveguide bend structure improves the transmission efficiency by adding air holes, in which a traveling direction is abruptly changed in the photonic crystal waveguide in the related art. That is, the transmission efficiency is improved by adding the air holes to a photonic crystal waveguide 60° bend structure.
However, since traveling modes of the light in the strip waveguide and the photonic crystal waveguide are different from each other, mismatch of the modes occurs in a region where the waveguides contact each other. Furthermore, this mismatch of the modes causes coupling loss.